Sit on a well-inflated exercise ball. For information on what diameter ball to use, read "Ball Size Matters."
Place your hands behind your head, and walk your feet away from the ball so your torso starts to roll onto the ball. The ball should support your hips and the curve of your lower back. Your legs should form a bridge with your knees bent at right angles.
Exhale and lift your upper body by about 45 degrees, pulling the deep abs in toward the spine, and return to starting position. Don't yank your neck! Do 25 reps.